Temporal and spatial variations of CO2 diffuse volcanic degassing on Cuicocha Caldera Lake - Ecuador

Cuicocha Caldera is the youngest eruptive center of Cotacachi-Cuicocha Volcanic Complex, located at the north of Ecuador. The caldera contains a lake of 3.95 km(2) surface, and a maximum depth of 148 m. Cuicocha Lake is characterized by the presence of CO2 gaseous diffuse emissions, perceptible as bubbling zones. Since 2011, CO2 diffuse flux measurements have been performed in this lake using the accumulation chamber method. The data obtained from twenty surveys were processed by means of the Graphical Statistical Approach and the Sequential Gaussian Simulation. The results reveal that Cuicocha lake has released a total estimated amount of similar to 400 kt of CO2 in the period between March 2011 and May 2019, with an average rate of 135 t/day. Furthermore, the spatial and temporal analysis of the data made possible the understanding of the processes occurring in the lake: 1) Lake stratification caused by the seasons seem to favor CO2 accumulation in the hipolimnion and its posterior releasing. Minimum total flux values of similar to 50 t/day have been estimated during warm stratified periods and maximum flux values of similar to 170 t/day have been recorded during cold overturn periods. Additionally, at least two anomalous degassing episodes were identified in 2012-2013, seemingly associated to changes in the volcanic activity also detected through seismicity. 2) Cuicocha CO2 degassing seems to be controlled by the existence of diffuse degassing structures at the lake bottom, which correspond to high permeability zones resulting from the intersection between similar to NE-SW and similar to WNW-ESE oriented structures. We propose a conceptual model to explain the systematic apparition of CO2 anomalies on specific areas of the lake surface. (C) 2020 Published by Elsevier B.V.

Automated summary

Cuicocha Caldera is the youngest eruptive center of Cotacachi-Cuicocha Volcanic Complex in northern Ecuador, characterized by CO2 gaseous emissions in its lake. Through measurements and data analysis, it has been found that CO2 release in Cuicocha Lake is influenced by seasonal changes and diffusing structures at the lake bottom, with anomalies possibly related to volcanic activity and seismic events.